In response to RFA-AA-07-005, Mechanisms of behavior change in treatment of alcohol use disorders, this project examines readiness to change substance use as a key proximal, highly malleable cognitive factor underlying change in alcohol and other drug use. This study focuses on readiness to change substance use because it is hypothesized to precede and predict changes in substance use, and serves as a sensitive marker of treatment effect. An intensive assessment schedule will be used to determine how treatment (specific and non-specific effects) impacts readiness to change substance use among dually diagnosed (co-occurring substance use and psychiatric illness) adolescents admitted to intensive outpatient (IOP) treatment. Adolescents will be assessed starting immediately after the initial evaluation for treatment, prior to attending the first IOP session, after each IOP session, and monthly after the start of treatment through 6-month follow-up. Intensive assessment will be used to determine how manualized, group-based IOP treatment and other factors (e.g., co-occurring psychopathology, probation status) impact youths' readiness to change substance use. We will prospectively study 50 adolescents (age 14-18) recruited from an Adolescent Dual Diagnosis Clinic. Each adolescent will have a parent collateral informant. Clinicians will provide ratings of youth participation after each IOP session. The project addresses three specific aims: (1) track changes in adolescents' readiness to change substance use (e.g., motivation to abstain), a proposed mediator of change in substance use behavior, starting at the initial evaluation for treatment at an adolescent dual diagnosis clinic, immediately after each intensive outpatient (IOP) session attended, and monthly after the start of IOP through 6-month follow-up; (2) examine readiness to change substance use behavior as a mediator of treatment effects and substance involvement, and to identify patient characteristics and extra-treatment factors that influence readiness to change substance use pre-, during, and through 6-months after treatment entry; and (3) determine how change during and post treatment in one area of functioning (e.g., substance use behavior) is associated with functioning in another domain (e.g. co-occurring psychopathology). Results have important implications for improving the content and delivery of treatment provided to dually diagnosed youth. An important goal of addictions treatment is to increase and maintain patients' readiness to change substance use. This project will examine how treatment impacts readiness to change in adolescent dual diagnosis (substance use and co-occurring psychiatric illness) outpatients. Results have important implications for improving the design and delivery of treatment provided to dually diagnosed adolescents. [unreadable] [unreadable] [unreadable]